1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to a registration device which arranges a front end of a medium entering an image forming apparatus, and the image forming apparatus having the same.
2. Description of the Related Art
FIG. 1 is a view illustrating a sheet arranging process of a conventional image forming apparatus.
Referring to FIG. 1, a sheet P is picked up from a stacking portion 5 by a pickup roller 1 and fed to a feed roller 3. The feed roller 3 feeds the sheet P in accordance with a printing speed of an image forming unit 4. While conveying the sheet P from the stacking portion 5 to the feed roller 3, the sheet P may skew. The skew of the sheet P may worsen if a parallel arrangement between the feed roller 3 and the image forming unit 4 is changed upon assembly of the image forming apparatus.
In order to print a good quality image, an arranging process for straightening out the skew of the sheet P is carried out. An arranging process in a conventional image forming apparatus will now be described in brief with reference to FIG. 1. While the sheet P is conveyed from the stacking portion 5 to the feed roller 3, the feed roller 3 rotates in a reverse direction to a conveying direction of the sheet P. Then, although a front end of the sheet P reaches the feed roller 3, the sheet P is blocked by the feed roller 3 and is not conveyed. In this state, if the pickup roller 1 further rotates, the sheet S bends as shown by a dotted line in FIG. 1, so that the front end of the sheet P is arranged at the feed roller 3. Then, the feed roller 3 is forwardly rotated to convey the sheet P to the image forming unit 4.
The conventional apparatus has the following problems. First, if the parallel relationship between the feed roller 3 and the image forming unit 4 changes when assembling the image forming apparatus, the feed roller 3 is reversely rotated to arrange the sheet P, thereby requiring more time to arrange the sheet and thus hindering high speed printing. Second, if the parallel relationship between the feed roller 3 and the image forming unit 4 changes when assembling the apparatus, the skew of the sheet P becomes worse. The front end of the sheet P is damaged during the reverse rotation of the feed roller 3, so paper jams may result. Third, it is very difficult to reversely rotate, stop, and again forwardly rotate the feed roller 3 to arrange the sheet, due to inertia of the feed roller 3. A load is applied to a motor (not shown) for driving the feed roller 3.
In addition, as the printing speed of the image forming apparatus increases, it becomes more difficult to forwardly or reversely rotate the feed roller 3. In this case, the rotational speed of the feed roller 3, which is reversely rotated, gradually decreases and the feed roller 3 stops rotating. Then, the feed roller 3 is again forwardly rotated, and the rotational speed of the feed roller 3 is gradually increased. Although such deceleration and acceleration processes may be adopted, the printing speed of the image forming apparatus decreases due to the time required by the deceleration and acceleration process. Finally, when the sheet is printed at high speed, there is no time to arrange the sheet P by forwardly or reversely rotating the feed roller 3.
Accordingly, there is a need for a registration device configured to improve high-speed operations of the image forming apparatus.